Micromirror systems with electrodes configured for sequential mirror attraction

ABSTRACT

Micromirror devices, especially for use in digital projection are disclosed. Other applications are contemplated as well. The devices employ a superstructure that includes a mirror supported over a hinge set above a substructure. Various improvements to the superstructure over known micromirror devices are provided. The features described are applicable to improve manufacturability, enable further miniaturization of the elements and/or to increase relative light return. Devices can be produced utilizing the various optional features described herein, possibly offering cost savings, lower power consumption, and higher resolution.

CROSS-REFERENCE TO RELATED APPLICATION

This is a Continuation application of U.S. patent application Ser. No.10/269,763 filed on Oct. 11, 2002 (now U.S. Pat. No. 6,825,968).

FIELD OF THE INVENTION

The present invention generally relates to the field of spatial lightmodulators that can form optical images by the modulation of incidentlight. The invention may involve micro electro-mechanical systems (MEMS)in the form of micromirror device arrays for use in optical display,adaptive optics and/or switching applications. Optionally, the inventionalso comprises individual or isolated micromirror elements.

BACKGROUND

Generally, MEMS devices are small structures, typically fabricated on asemiconductor wafer using processing techniques including opticallithography, metal sputtering, plasma oxide deposition, and plasmaetching developed for the fabrication of integrated circuits.Micromirror devices are a type of MEMS device. Other types of MEMSdevices include accelerometers, pressure and flow sensors, fuelinjectors, inkjet ports, and gears and motors—to name a few. Micromirrordevices have already met with a great deal of commercial success.

Micromirror devices are primarily used in optical display systems. Thelarge demand for micromirror-based display systems is a result of thesuperior image quality the systems can provide. Commercial andhome-theater segments drive this facet of market demand. Other marketsegments are characterized by cost concerns more than image qualityconcerns. Since these devices are produced in bulk on semiconductorwafers, they take advantage of the same wafer processing economies ofscale that characterize the semiconductor industry, thus making the saleof these devices competitive at all price points.

In display systems, the micromirror device is a light modulator thatoften uses digital image data to modulate a beam of light by selectivelyreflecting portions of the beam of light to a display screen. Whileanalog modes of operation are possible, many micromirror devices areoperated in a digital bistable mode of operation.

The unique properties of current and future micromirror-based displaysystems will allow them to capture market share for applicationsincluding theatre and conference room projectors, institutionalprojectors, home theater, standard television and high definitiondisplays from various lesser-quality solutions including liquid crystaldisplay (LCD) and cathode ray tube (CRT) type systems. Micromirror-baseddisplay systems now offer compact, high resolution and high brightnessalternatives to other existing technology.

Presently, such systems are further characterized by: all-digitaldisplay (mirror control is completely digital except for the possibleA/D conversion necessary at the source); progressive display (removinginterlace display artifacts such as flicker—sometimes necessitating aninterlace to progressive scan conversion); fixed display resolution (thenumber of mirrors on the device defines the mirror array resolution;combined with the 1:1 aspect ratio of the on-screen pixels, the fixedratio presently requires re-sampling of various input video formats tofit onto the micromirror array); digital color creation (spectralcharacteristics of color filters and lamp(s) are coupled to digitalcolor processing in the system); and digital display transfercharacteristics (micromirror device displays exhibit a linearrelationship between the gray scale value used to modulate the mirrorsand the corresponding light intensity, thus a “de-gamma” process isperformed as part of the video processing prior to display).

MEMS display devices have evolved rapidly over the past ten to fifteenyears. Early devices used a deformable reflective membrane that waselectrostatically attracted to an underlying address electrode. Whenaddress voltage was applied, the membrane would dimple toward theaddress electrode. Schlieren optics was used to illuminate the membraneand create an image from the light scattered by the dimpled portions ofthe membrane. The images formed by Schlieren systems were very dim andhad low contrast ratios, making them unsuitable for most image displayapplications.

Later generation micromirror devices used flaps or cantilever beams ofsilicon or aluminum, coupled with dark-field optics to create imageshaving improved contrast ratios. These devices typically used a singlemetal layer to form the reflective layer of the device. This singlemetal layer bent downward over the length of the flap or cantilever whenattracted by the underlying address electrode, creating a curvedsurface. Incident light was scattered by this surface thereby loweringthe contrast ratio of images formed with flap or cantilever beamdevices.

Devices utilizing a mirror supported by adjacent torsion bar sectionswere then developed to improve the image contrast ratio by concentratingthe deformation on a relatively small portion of the reflecting surface.These devices used a thin metal layer to form a torsion bar, which isoften referred to as the hinge, and a thicker metal layer to form arigid member. The thicker member typically has a mirror-like surface.The rigid mirror remains flat while the torsion hinges deform,minimizing the amount of light scattered by the device and improving itscontrast ratio. Though improved, the support structure of these deviceswas in the optical path, and therefore contributed to an unacceptableamount of scattered light.

The more successful micromirror configurations have incorporated a“hidden-hinge” or concealed torsion/flexure member(s) to further improvethe image contrast ratio by using an elevated mirror to block most ofthe light from reaching the device support structures. Because themirror support structures that allow it to rotate are underneath themirror instead of around the perimeter of the mirror, more of thesurface area of the device is available to reflect light correspondingto the pixel image. Since much of the light striking a concealed-flexuremicromirror device reaches an active pixel surface and is either used toform an image pixel or reflected away from the image to a light trap,the contrast ratio of such a device is much higher than the contrastratio of other known devices.

Some of this progression is published on the world wide web site ofTexas Instruments. Further review and technical details as may beemployed (including in the present invention) are presented in MEMS andMOEMS Technology and Applications, by P. Rai-Choudhury, 169–208 (SPIEPress, 2000).

Despite such advances in design, several aspects of known micromirrordevices may be further improved. First, general considerations ofmanufacturability, which play directly into cost, may be improved. Forinstance, increasing the yield of devices (in the form of pixels thatpass functional criteria) from a given processed wafer offers bothimprovement in product quality and cost savings. In addition, lesscomplicated manufacturing procedures, including a process requiringfewer masks or steps for production of micromirror devices would bedesirable.

Still further, performance aspects of existing micromirror devices canbe improved. One such aspect concerns increasing the percentage of lightreturn from the micromirrors. Another involves the angular displacementthat can be realized in deflecting a given mirror. The overalldeflection ability or total angular resolution can be particularlyimportant in terms of optical switching applications as well as in thecontrast ratio of image production.

Yet another performance aspect in which improvement is possible concernspower consumption. Micromirror devices currently in production for SVGAapplications include over half a million active mirrors, SXGAapplications require over one point three million active mirrors. Sincepowering so many elements has a cumulative effect, addressing powerconsumption issues will be of increasing importance in the future as thenumber of pixels employed in image creation continues to increase.

Yet another avenue for micromirror device improvement lies in continuedminiaturization of the devices. In terms of performance, this canimprove power consumption since, smaller distances between parts andlower mass parts will improve energy consumption and increase displaysystem resolution by providing a micromirror device with greater mirrordensity given overall package size constraints. In terms ofmanufacturing, continued miniaturization of mirror elements can offer agreater number of micromirror systems for a wafer of a given size.

Various aspects of the present invention offer improvement in terms ofone or more of the considerations noted above. Of course, certainfeatures may be offered in one variation of the invention, but notanother. In any case, features offered by aspects of the presentinvention represent a departure from structural approaches representedby the Texas Instruments DMD™. The inventive features represent analtogether distinct evolutionary branch of “hidden-hinge” orconcealed-flexure micromirror device development, rather than meresequential refinement of features as may be noted in the development ofthe Texas Instruments DMD™ element described in detail below. Thedivergent approaches marked by aspects of the present invention offer acompetitive edge to the present invention to benefit consumers in any ofa number of ways.

SUMMARY OF THE INVENTION

The present invention involves micromirror structures, optionally usedin display systems. Micromirror array devices according to the presentinvention generally comprise a superstructure disposed over asubstructure including addressing features. Features of thesuperstructure set upon and above the substrate include electrodes,hinges, mirrors/micromirrors, support members or portions thereof.

The electrodes used to actuate the mirrors are arranged so theyprogressively attract mirror portions. This may be accomplished usingelectrode portions that step down from a higher level close to amirror's hinge to a lower outer level. With a portion of each electrodebeing closer to said mirror closer to a center of said mirror andanother portion of each electrode being farther from said mirror furtherfrom said mirror center both sequential attraction of a mirror by saidelectrode portions and clearance for allowing adequate mirror tilt ispossible.

Electrodes thus configured may be supported in any manner, whetherprovided by a unitary structure or separately built-up portions. Aplurality of discrete planar levels (as few as two) may be provided, oreven one or more angled electrode surfaces. Electrode variations inwhich high multiples of levels or stages are employed will model a trueangular surface. Such angular and even curved surfaces are within thescope of the invention.

Whereas the referenced Texas Instruments DMD™ employs electrodes atdifferent heights, the attraction effected is not sequential in thesense discussed herein. What is more, according to a preferred variationof the present invention, only a single surface (the underside of themirror) interacts electrostatically with the different heightelectrodes. Systems thus provided, that still allow adequate forcing ofits mirror elements to achieve sufficient tilt angles in opposition torestoring forces, can still be manufactured with a five mask process (incontrast to the six mask process of the referenced Texas Instrumentsdevice).

The present invention includes any of these improvements describedeither individually, or in combination. Systems employing micromirrordevices including the improved superstructure form aspects of theinvention as does methodology associated with the use and manufacture ofapparatus according to the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1–8H represent information known in the art, in which FIGS. 6 and8A–8H represent aspects of a known micromirror device. The featuresshown in the other figures may be used in the present invention. FIGS.9A–15H show features particular to the present invention. FIGS. 11A and11B compare micromirror devices according the present invention againstthe device shown in the referenced figures. Certain aspects of thefigures diagrammatically represent the present invention, while othersare indicative of preferred relations. Regardless, variation of theinvention from what is shown in the figures is contemplated.

FIGS. 1A and 1B are side views illustrating bi-stable micromirroroperation.

FIG. 2 is a perspective-combined view illustrating the projection ofthree pixels utilizing a portion of a micromirror device display system.

FIG. 3 is a perspective view illustrating grayscale image production fora single line of mirrors in a micromirror device utilizing pulse widthmodulation (PWM).

FIG. 4 is a perspective view of an exemplary color micromirrorprojection system.

FIG. 5A is a perspective view of a micromirror device based projector;FIG. 5B is a perspective view of a micromirror device based projectiontelevision.

FIG. 6 is an exploded perspective view of a DMD™ element.

FIG. 7 is a circuit diagram showing a manner of addressing a micromirrordevice array.

FIGS. 8A–8H are perspective views showing the micromirror elements ofFIG. 6 at various stages of production.

FIG. 9A shows a perspective view of a micromirror element according tothe present invention; FIG. 9B shows the element in FIG. 9A without amirror; FIG. 9C shows the element of FIG. 9A from the side. FIGS.9A′–9C′ show the same views of another variation of the inventionemploying an alternate mirror support approach. FIGS. 9A″–9C″ show thesame views of a further variation of the present invention that employsa hexagonal mirror.

FIGS. 10A–10G are perspective views showing the micromirror element(s)of FIGS. 9A–9C at various stages of production.

FIG. 11A is a top view comparing the DMD™ of FIG. 6 with the micromirrordevice of FIG. 8; FIG. 11B is a perspective view of arrays of elementsas shown in FIG. 11A.

FIGS. 12A–12C show different mirror support configurations according tothe present invention.

FIGS. 13A and 13B show optional manners of producing support portionswith and without a base, respectively.

FIGS. 14A–14C show different mirror configurations in an intermediatestage of production.

FIGS. 15A–15H are side views of various electrode configurationsemploying a variety of levels, shapes and support approaches.

DETAILED DESCRIPTION

In describing the invention in greater detail than provided in theSummary above, applicable technology is first described. This discussionis followed by description of a known micromirror device and its mannerof production. Then a variation of a micromirror device according to thepresent invention is disclosed, as well as a preferred manner ofproduction. Next, comparative views of the known and inventivemicromirror devices are described. Finally, additional optional aspectsof the present invention are described, including various optionalsupport, micromirror and electrode configurations.

Before the present invention is described in such detail, however, it isto be understood that this invention is not limited to particularvariations set forth and may, of course, vary. Various changes may bemade to the invention described and equivalents may be substitutedwithout departing from the true spirit and scope of the invention. Inaddition, many modifications may be made to adapt a particularsituation, material, shape of design, composition of matter, process,process act(s) or step(s), to the objective(s), spirit or scope of thepresent invention. All such modifications are intended to be within thescope of the claims made herein.

Methods recited herein may be carried out in any order of the recitedevents which are logically possible, as well as the recited order ofevents. Furthermore, where a range of values is provided, it isunderstood that every intervening value, between the upper and lowerlimit of that range and any other stated or intervening value in thatstated range is encompassed within the invention. Also, it iscontemplated that any optional feature of the inventive variationsdescribed may be set forth and claimed independently, or in combinationwith any one or more of the features described herein.

All existing subject matter mentioned herein (e.g., publications,patents, patent applications and hardware) is incorporated by referenceherein in its entirety except insofar as the subject matter may conflictwith that of the present invention (in which case what is present hereinshall prevail). The referenced items are provided solely for theirdisclosure prior to the filing date of the present application. Nothingherein is to be construed as an admission that the present invention isnot entitled to antedate such material by virtue of prior invention.

Reference to a singular item, includes the possibility that there areplural of the same items present. More specifically, as used herein andin the appended claims, the singular forms “a,” “and,” “said” and “the”include plural referents unless the context clearly dictates otherwise.It is further noted that the claims may be drafted to exclude anyoptional element. As such, this statement is intended to serve asantecedent basis for use of such exclusive terminology as “solely,”“only,” or “lacking” and the like in connection with the recitation ofclaim elements, or use of a “negative” limitation.

Unless defined otherwise below, all technical and scientific terms usedherein have the same meaning as commonly understood by one of ordinaryskill in the art to which this invention belongs. Still, certainelements may be defined herein for the sake of clarity, possiblyproviding an alternate meaning.

Turning now to FIGS. 1A and 1B, bistable operation of a micromechanicallight modulator 2 is shown. The device comprises a mirror portion 4, ahinge portion 6 and electrode portions 8 set upon a substrate 10.

In FIG. 1A, the mirror is shown rotated or flexed about a hinge portion6 in a clockwise direction from a horizontal position. The hinge isconfigured to provide a mechanical restoring force in returning frommirror rotation. Mirror rotation occurs as a result of electrostaticattraction between at least the mirror portion 4 and an electrodeportion 8 of the device located above a substrate 10 which carries eachof the elements.

Thus attracted, the mirror is pinned at a stable, minimum potentialenergy state. FIG. 1B shows the mirror deflected to a second minimumpotential energy state opposite a second electrode. Operation of amicromirror device mirror between two such full-angle states representswhat is referred to as “bistable” operation. Such operation is employedin a digital mode.

Digital operation sometimes involves employing a relatively largeaddress voltage to ensure the mirror is fully deflected. Addresselectrodes are driven by underlying logic circuitry. A bias voltage,usually a positive voltage, is typically applied to the mirror metallayer to control the voltage difference between the address electrodesand the mirrors. Setting the mirror bias voltage above what is termedthe “threshold voltage” of the device ensures the mirror will fullydeflect toward the address electrode, even in the absence of an addressvoltage. Where a large bias voltage is employed, lower address voltagesmay be used since the address voltages need only cross a meta-stablepoint to enter an opposite bi-stable minimum potential energy state.

Micromirror devices may also be operated in analog mode. Sometimesreferred to as “beam steering,” this operation involves charging addresselectrode(s) to a voltage corresponding to the desired deflection of themirror. Light striking the micromirror device is reflected by the mirrorat an angle determined by the deflection of the mirror. A ray of lightreflected by an individual mirror is directed to fall outside theaperture of a projection lens, partially within the aperture, orcompletely within the aperture of the lens, depending on the voltageapplied to the address electrode(s). The reflected light is focused bythe lens system onto an image plane. Each individual mirror pixelcorresponds to a pixel on the image plane. As the ray of reflected lightis moved from completely within the aperture to completely outside theaperture, the image location corresponding to the mirror dims, creatingcontinuous brightness levels.

Note also, that both digital and analog micromirror device operation isapplicable in the context of such devices used for optical switchingapplications. That is to say, micromirror devices (especially thoseproduced according to the present invention) lend themselves todirecting light from one path to another to optically connect anddisconnect pathways as desired.

Yet, for the sake of discussion in introducing aspects of the inventionin contrast to known designs, FIG. 2 illustrates an approach toproducing images in a digital mode of micromirror device operation.Incident light from a light source 12 striking a mirror 2 rotated towardthe light source is reflected to pass through a lens 14 and be displayedas a corresponding bright pixel 16 on a screen or the like (turnedupward relative to the other components shown for ease of viewing). Incontrast, mirrors rotated away from the light source reflect light awayfrom the projection lens into a light trap 18 leaving a correspondingdark pixel 20 at the projection image surface. Mirrors rotated toproduce a bright pixel may be regarded as “on,” while those positionedto leave a pixel dark may be regarded as “off.”

FIG. 3 illustrates a manner in which intermediate pixel brightness maybe obtained. Digital mode micromirrors employ pulse width modulationtechniques to rapidly rotate a mirror on and off to vary the quantity oflight reaching the image plane. The human eye integrates the lightpulses and the brain perceives a flicker-free intermediate brightnesslevel. In FIG. 3, an active row of micromechanical light modulatorelements 2 are depicted, forming a portion of a larger array 22.Directional markers 24 indicate the location of corresponding pixelswithin a projected pixel row 26 opposite a lens 14. A full-intensitybright pixel 16 is displayed by constant application of light rays 28. Adark pixel 20 is provided by leaving the corresponding reflectiveelement 2 “off” so that essentially no light reaches the projectiontarget. Pixels of intermediate intensity 30 are provided by applicationof intermediate lighted intervals by turning “on” and “off” thecorresponding micromirror element 2.

FIG. 4 shows a digital projection subsystem 32 in which the digitaloperation principle(s) discussed above are applied to project a cogentimage on a screen 34. The subsystem includes a light source 12 and aprojection lens 14 as well as a board or module 36 including a processor38, memory 40 and micromirror array 42 comprising light modulatingelements 2. The micromirror device shown is “packaged” in that the MEMSportion micromirror array 22 element of the device is set within ahousing 44 sealed by a window 46.

These components alone, perhaps with intermediate optics to shape thelight emanating from source 12, would be sufficient to present agray-scale or “black and white” image. Additional components in the formof a color filter or “color wheel” 48 and optics for use therewithincluding a condensing lens 50 and a shaping lens 52 to focus andrestore a columnar light beam through colored sections of the lens asits rotates are provided. Through coordinated rotation on the wheel andactuation of the micromirror elements 2, full color synthesis ispossible.

Full-color images are generated by sequentially forming threesingle-color images. This process in concert with the former discussionof analog or digital methods of grayscaling gives many levels of shadingof each color. The viewer perceives a single, full color image from thesum of the three single-color grayscaled images.

In addition to color wheel approaches, others are known. In accordancewith known techniques, dedicated one-color or filtered light sources maybe provided instead of a color wheel, especially utilizing a pluralityof micromirror devices. Alternately, a color wheel may continue to beutilized with a plurality of micromirror devices in conjunction with acolor separating prism (not shown). Still further, a plurality ofmicromirror devices may be provided and used in conjunction with a lightsource, no color wheel, but with color filtering prisms.

The choice of optics may vary. Providing additional light sources and/oradditional micromirror arrays allows for image creation throughsuperposition offering the potential for greater brightness andresolution. Simply providing dedicated light sources for a singlemicromirror array may improve brightness as well. One limitation tocurrent micromirror device implemented solutions involves brightnesslevels. Since there is a practical limit to the brightness of a singlesource, one solution to this malady is to utilize multiple lightsources. Factors of greater cost/system complexity will typically beweighed in determining whether to implement these improvements in agiven system.

Regardless of the ultimate configuration selected, one of two mediaformats is preferably employed with the micromirror devices, thoughothers are possible. These are illustrated in FIGS. 5A and 5B. The firstfigure depicts a projector 54. The projector shown is suitable for thetypical consumer home-theater. Other devices that may incorporatesystems according to the present invention may be suitable for largervenues (i.e., staging events and cinema presentations), being configuredfor high light output and waste heat generation. The second figuredepicts a projection television 56. The television pictured is a rearprojection system, though other styles (e.g., front projection) may beemployed.

Whatever the case, such systems may be specifically designed for ordesigned around micromirror devices according to the present invention.Alternately, it is contemplated that a packaged “light engine” accordingto the present invention could be substituted into existing systems(with or without further modification or substituting the entire module36) to upgrade performance.

To appreciate the performance advantages available through variousaspects of the present invention, it is important to first appreciatethe structure of the above-referenced Texas Instruments devices that arebelieved to define the state of the art at the time of filing. FIG. 6shows a single mirror element 2 of an array in an exploded perspectiveview.

Several levels of structure are expressed. The bottom level is asemiconductor substrate 58 with electrode addressing circuitry 60provided thereon. The manner in which such circuitry is addressed(whether as provided in the referenced micromirror devices or thoseaccording to the present invention) is illustrated in FIG. 7. For thevarious rows and columns of micromirror elements 2, addressingarchitecture is shown that incorporates N addressing inputs 62 for every2N rows and 1 data input 64 for every 16 columns. Such substratematerial in various configurations, with a passivation layer includingvias to provide connectivity at selected locations/spacing iscommercially available.

Returning to FIG. 6, the physical alignment of superstructure componentsabove the address circuitry is such that, upon selection, addressvoltage is applied to the electrodes of the device. The bias voltagediscussed above is applied to the mirror by way of intermediatestructures connected to a bias/reset bus 66 provided upon substrate 58.

Hinge supports 68 are set above the bias bus, and supported above bus 66by substantially square, columnar via-based supports 70. (The finalalignment of these components and others is indicated in dashed lines.)The support posts are produced by deposition within a hole providedwithin a sacrificial layer of material in an intermediate stage ofdevice production. Accordingly, they are not solid, but rather hollowuntil the solid base portion 72, with a closed outer wall or periphery.The hinge supports are attached to hinge segments or portions 74 whichare in-turn attached to a yoke 76. The corners of the yoke are providedwith spring tips 78. The spring tips provide bumpers to cushion ormoderate contact between the yoke and bias bus upon full mirroractuation, rather than having to precisely control voltages or rely onother interfering contact. While potentially useful, it is contemplatedthat micromirror devices according to the present invention may or maynot make use such features.

Above the yoke, micromirror element 2 includes a mirror 80. The mirroris connected to the yoke by way of a via-type support 70 like thoseprovided for the hinge supports, leaving a hole 118 in the mirror face.By way of the connecting structures, each of the mirror, yoke, hingesand hinge supports are charged to the bias voltage of bus 66.

To actuate the device, a voltage is applied to the electrodes 82 and 84that electrostatically attract both the mirror and yoke, respectively.The electrodes are set at two levels. The higher-up outer electrodeportions 82 are electrically connected to the lower electrode portions84 by way of another connecting columnar via 70. This combination ofelements is placed in electrical contact with the addressing circuitryby a filled-in via 86 in the base of each electrode portion 84. Theupper electrodes are positioned to attract the mirror, whereas the lowerelectrodes are positioned to attract the yoke.

The manner of producing the superstructure of micromirror device 2 isrepresented in FIGS. 8A–8H. The stages shown are indicative of actiontaken after intermediate masking steps between material deposition(sacrificial material or structural material) and sacrificial materialremoval. To most clearly portray the structure being produced, theperspective view shown takes the device across the sectional line shownin FIG. 6 and tilts the structure.

In FIG. 8A, a portion of bus 66 and a lower electrode 84 are shown,formed by a conductive material. These are provided by materialdeposited over substrate 10, with the overlaid material strategicallyetched away. The raised portions will have been covered by a protectionlayer, configured using a first mask 88 (diagrammatically pictured). Thesubstrate comprises the addressing circuitry covered by a passivationlayer, the layer having holes strategically placed to provide accessvias to the underlying circuitry. The vias are filled-in to provideelectrical connections 86 between the substrate and electrodes as notedabove with respect to FIG. 6.

FIG. 8B shows a layer of sacrificial material 90, deposited over thestructure in FIG. 8A. Via column holes 92 are provided, again byselectively etching the material in connection with a second mask 94.

In FIG. 8C another layer of conductive material 96 suitable for use inproducing hinge sections 74 and spring tips 78 is laid-down. Followingthis, a third mask 98 is employed in setting a protective layer such asan oxide (not shown) over the regions of layer 96 serving as hingeprecursors 100, and spring tip precursors 79.

In FIG. 8D, another layer of conductive material 102 is depositedthereon. A fourth mask 104 is utilized to form a protective layer (notshown) over the regions of layer 102 serving as hinge support precursors106, a beam or yoke precursor 108 and upper electrode precursor(s) 110.

Both the hinge metal layer 96 and yoke/electrode metal layer 102 fillvia holes 92, providing columnar support portions 70. The portions ofthe material layers not protected during processes involving the thirdand fourth masks are selectively etched as shown in FIG. 8E to definehinge supports 68, hinges 74, yoke 76 and upper electrode portions 82.

FIG. 8F shows the micromirror device in another intermediate stage ofproduction with another layer of sacrificial material 112. This layer isdeposited over the structure in FIG. 8E. It includes a via column hole96, patterned utilizing a fifth mask 114. When a mirror material layer116 is deposited over sacrificial layer 112 as shown in FIG. 8G, viahole 96 is partially filled in, providing support column 70, but leavinga hole or opening 118 in what is to become the “face” of the mirrorelement. Following a deposited metal oxide layer (not shown), a sixthand final mask 120 is used to pattern and define a mirror precursorregion 122 and adjacent borders indicated by dashed lines, the latterbeing removed to form spaces between adjacent mirrors 80 in a completemicromirror array. Finally, FIG. 8H shows the micromirror element 2 ascompleted, with all sacrificial material removed to release thestructure.

The details of the materials employed, intermediate preparation stepsand further constructional details associated with the methodologydescribed are known by those with skill in the art, within the scope ofreasonable experimentation by the same and/or may be appreciated byreference to background noted above or the following U.S. patents: U.S.Pat. No. 5,083,857 to Hombeck, entitled “Multi-level Deformable MirrorDevice”; U.S. Pat. No. 5,096,279 to Hombeck, et al., entitled “SpatialLight Modulator and Method”; U.S. Pat. No. 5,212,582 to Nelson, entitled“Electrostatically Controlled Beam Steering Device and Method”; U.S.Pat. No. 5,535,047 to Hombeck, entitled “Active Yoke Hidden HingeDigital Micromirror Device”; U.S. Pat. No. 5,583,688 to Hombeck,entitled “Multi-level Digital Micromirror Device”; U.S. Pat. No.5,600,383 to Hombeck, entitled “Multi-level Deformable Mirror Devicewith Torsion Hinges Placed in a layer Different From the Torsion BeamLayer”; U.S. Pat. No. 5,835,256 to Huibers, entitled “Reflective spatialLight Modulator with Encapsulated Micro-Mechanical Element”; U.S. Pat.No. 6,028,689 to Michalicek, et al., entitled “Multi-MotionMicromirror”; U.S. Pat. No. 6,028,690 to Carter, et al., entitled“Reduced Micromirror Mirror Gaps for Improved Contrast Ratio”; U.S. Pat.No. 6,323,982 to Hombeck, entitled “Yield Superstructure for DigitalMicromirror Device”; U.S. Pat. No. 6,337,760 to Huibers, entitled:“Encapsulated Multi-Directional Light Beam Steering Device”; U.S. Pat.No. 6,348,907 to Wood, entitled “Display Apparatus with DigitalMicromirror Device”; U.S. Pat. No. 6,356,378 to Huibers, entitled“Double Substrate Refletive Spatial Light Modulator”; U.S. Pat. No.6,369,931 to Funk, et al, entitled “Method for Manufacturing aMicromechanical Device”; U.S. Pat. No. 6,388,661 to Richards, entitled“Monochrome and Color Digital Display System and Methods”; U.S. Pat. No.6,396,619 to Huibers, et al., entitled “Deflectable Spatial LightModulator Having Stopping Mechanisms”. In any case, micromirror devicesaccording to the present invention may be produced and/or operatedaccording to the same details or otherwise.

Regarding the features of the present invention, FIG. 9A shows apreferred micromirror element 124 per the invention. The variation ofthe invention shown includes each of the optional features that may beemployed, though not all such features need be provided in a givenproduct. FIG. 9B shows the micromirror device 124 in FIG. 9A minus itsmirror. FIG. 9C shows the same from the side.

Optional features of the invention that may be employed together orindividually break down into three basic groups. A first group concernssupporting a mirror portion 126 at its sides; a second group concernsproviding electrodes 128 adapted for sequential attraction of themirror; and a third group concerns supporting various componentsincluding the mirror, electrode portions and/or hinge portions 130 withopen support structures. These features are addressed variously in thefollowing description.

The mirror shown in FIG. 9A has an uninterrupted “face” in that itsreflective surface is unbroken as compared to device 2 of FIGS. 6 and 8.While the “potential face” or “prospective face” of the mirror(indicated by solid and dashed lines together) may be somewhat largerthan the actual face of the mirror (the area indicated by solid linesalone), “dim” or “dead” space 132 resulting, generally, in lightscattering may be reduced. As described below, such space may beminimized or even eliminated according to an aspect of the presentinvention.

First, general features of element 124 under the mirror are described.One such aspect concerns the manner in which mirror 126 is attached toits hinge. Supports 134 on opposite sides of mirror element 126 secureit to hinge portions 130. The hinge portions may comprise individualsegments, or may be part of a unitary structure. In any case, the hingedefined is attached to substrate 136 by a bridge-type support 138. Thesupport is preferably open underneath the hinge center 140, which isattached to a spanning segment 142 between vertical support segments144. Feet 146 may additionally be provided to stabilize the supportstructure. Yet another option is to produce support segments 144 at anangle relative to the surface of the substrate (i.e., having bothvertical and horizontal components).

Likewise, support 134 may be set at an angle with respect to thesubstrate. Yet, it is more preferable that support(s) be providedorthogonally as shown. A base 148 of each support 134 may directlyconnect each hinge portion 130. However, it may be preferred that anintermediate layer or nub 150 of material (e.g., serving as a bondinginterface) is employed.

In any case, the device is configured so that the hinge is set somedistance (as little as about 0.1 micron, or less) above the surface ofsubstrate 136 and mirror 126 is set some distance (as little as about0.1 micron, or less) above the hinges (as little as about 0.2 micron, orless, above the surface of substrate 136). Avoidance of a yoke allowscreation of very low profile micromirror devices by the invention thatare still able to attain high deflection angles (typically about +/−10deg., even upwards of about +/−15 deg., to about +/−20 deg. or more). Ofcourse, mirror/micromirror devices according to the present inventionmay be advantageously manufactured on a larger scale (even using MEMStechniques)—possibly utilizing other actuation techniques, includingelectromagnetic, electromechanical, thermo-mechanical or piezo-basedapproaches—especially for non-projection technology.

An aspect of the invention that facilitates provision of adequateelectrostatic attraction in response to hinge restoring forces thatincrease with angular deflection has to do with the configuration ofelectrodes 128. The electrodes may be configured with a plurality ofportions 152 and 154 (or more) at different levels. Whether provided ina series of steps by continuous members (as shown with a support portion156 between each stage 152/154), by steps formed with discrete membersor a continuous angled member, the electrodes are configured so thatportions further from the center or point of rotation of the mirror areat a lower level.

The electrode configuration shown with higher portions closer to thecenter and lower portions more distant provides clearance for the mirroras it is tilted at an angle. Furthermore, the configuration provides forsequential attraction of mirror 126. When the mirror is angled away froma set of electrodes, the upper electrode portion is the first to exertsignificant attractive electrostatic force on the mirror (in light ofthe inverse squared relationship between electrostatic attraction anddistance between objects). As the upper electrode portion(s) effectivelyattract the mirror drawing inward, the influence of the electrode lowerportion(s) increase. Further aiding attraction of the mirror to its fullangular displacement is the increased mechanical advantage or lever armoffered at more remote regions of the mirror interacting with lowerelectrode portion 152.

The manner in which a micromirror device 124 according to the presentinvention may be produced is illustrated in FIGS. 10A–10G. Of course,the process steps employed will vary depending on which inventivefeatures are actually employed in a given variation of the invention.But again, a most preferred approach is shown.

In FIG. 10A, a sacrificial layer of material 158 is set upon substrate136. It is patterned with a first mask 210 to define openings 160 and asubstrate-level portion 162 upon etching. In FIG. 10B, a hinge metallayer 164 is deposited over the entire surface including a portion ofthe sacrificial layer. A second mask 166 is utilized in defining apassivation layer (not shown) over the region(s) of layer 164 serving asa hinge precursor region 168. Metal layer 164 fills in via 206 providedin substrate 136 to form a connection 208 between underlying addresscircuitry beneath an oxide layer of the substrate. The same approach toaddressing and substrate construction may be employed as describedabove, or another manner of electrical control of device superstructureproduced may be utilized. This holds true with respect to connectivitybetween the device elements as well as the configuration of substrate136.

As shown in FIG. 10C, a thicker layer of conductive material 170 isdeposited over the hinge material. This layer builds-up the electrodes128 and further fills openings 160, defining a support precursor region172 for hinge portions 130. Layer 170 also further fills in via 206 andconnecting structure 208. A third mask 174 is employed to define aprotective layer (not shown) over the region of layer 170 serving aselectrode precursor(s) 176.

In FIG. 10D, layers 164 and 170 are shown selectively etched to revealhinge 130, support spanner 142, and electrode portions 152 and 154. Asshown in FIG. 10E, these structures are then covered by anothersacrificial layer 178. A fourth mask 180 is used to pattern sacrificiallayer 178 to form support precursor regions 182 upon etching thesacrificial layer.

FIG. 10F shows sacrificial layer 178 as it is selectively etched, andthen coated with a layer 184 of conductive material suitable to serve asa mirror (or a substrate that may be subsequently coated with a highlyreflective metal or dielectric material). A fifth mask 186 is used inorder to define a passivation layer over mirror precursor regions 188 tobe retained, but not the adjacent borders 190, which are removed to formspaces between adjacent micromirrors 126.

FIG. 10G shows a micromirror element 124 according to aspects of theinvention after all sacrificial materials have been removed. Asdiscussed above, the mirror is supported at or along its opposite sidesor edges by supports attached to a hinge, which is in turn supportedabove the device substrate. In addition to being placed at oppositesides/portions of the mirror, the support members may be characterizedas being “open” in nature. Progressive or dual-stage electrodes areshown as well.

It is further noteworthy that a micromirror device produced according tothe methodology described merely requires 5 masks—i.e., as constructedon a pre-fabricated substrate. In contrast, the Texas Instruments DMD™is produced using 6 masks under the same conditions. Thus, themethodology according to the present invention is highly advantageousfrom both fabrication cost and device yield standpoints.

Still, a micromirror device according to the present can be producedwith the same pixel dimensions as known devices. In doing so, a deviceaccording to the present invention will offer a performance benefits atleast in terms of light return. Reasons for this advance are discussedbelow.

Before such discussion, it is helpful to first consider a side-by-sidecomparison of micromirror elements as provided in FIGS. 11A and 11B. ATexas Instruments DMD™ element 2 is shown from above on the left with amicromirror device 124 according to the present invention next to it.The size differences between the two are immediately apparent. Usingpresent techniques, micromirror devices according to certain aspects ofthe present invention may be made smaller than the referenced devices bybetween about 25% and about 65% or more (i.e., devices according to thepresent invention may be about 75% to about 35% of the size of knowndevices) due the absence of a yoke layer in order to allow for a smallersacrificial layer gap—while still employing a plurality of electrodelevels.

Reduction of the support footprint (pixel size) allows for a smallermirror with the same hinge length. The reduced sacrificial layer gapallows for overall thinner structure, which reduces the horizontalpivoting space necessary to deflect a mirror, thus reducing the gapnecessary between adjacent mirrors.

Generally, mirrors elements employed in the present invention can bemade smaller than DMD-sized mirrors that have roughly a 19 microndiameter. Mirrors/pixel elements according to the present invention mayadvantageously be produced at less than about 10 microns in diameter. By“diameter,” what is meant is the distance across any long axis that maybe defined; stated otherwise, the diameter will correspond to that ofany circle in which the structure can be circumscribed.

FIGS. 9A′–9C′ show components of another device 124 constructed using ameans or approach to mirror support somewhat different from thatdiscussed above. Still, such devices may advantageously be selected foruse in a micromirror device array and present many of the same benefitsas elements constructed according to FIGS. 9A–9C. Yet, the micromirrordevice element shown in FIGS. 9A′–9C′ may be desired from amanufacturing perspective, or for one or more other reasons depending onthe circumstances.

The support configuration shown may be produced in connection with amodified version of the five-mask process described above, whereindifferences in production methodology will be readily apparent to onewith skill in the art. Basically, in this variation of the invention,columnar supports or posts 212 are utilized which may be created byfilling in vias produced in sacrificial material. As in other variationsof the invention pictured, each of the pair of supports is positionedopposite one another and across the body of mirror 126. Supports 212 areshown to have a wall 214 at the edge of mirror 126 (each may have fourwalls or more or may define curved surfaces—depending on the originalvia shape that is filled-in to create the structure). Yet, the supportsmay be inset from the side/corner or edge of a mirror (depending on thestyle of micromirror device chosen) to which they are closest. However,it may be preferred to position supports 212 in such a way as tomaximize hinge or torsion member length in view of the mirrorstyle/format selected (i.e., square with corner support positions,hexagonal with corner supported positions, hexagonal with side supportpositions, etc.). In which case, the base of each support (or anintermediate structure) will be positioned at the end of any hingeportions. However configured, supports 212 will generally be positionedoutside of the hinge support member 138 or members.

FIGS. 9A″–9C″ provide details of a hexagonal-shaped mirror supported atopposite corner positions. Its construction and appearance closelyresemble the micromirror elements 124 shown in FIGS. 9A–9C. However, thehexagonal mirror format offers certain advantages in use. For one, theycan be closely packed in a manner like a honeycomb, where sequentialrows (or columns) overlap. Such overlap provides the ability in imagecreation to mimic higher resolution output where there is overlap. Theprinciples of such operation are well documented and may be understoodin reference to U.S. Pat. No. 6,232,936 to Gove, et al., entitled “DMDArchitecture to Improve Horizontal Resolution”. Further potentialadvantages associated with the mirror format shown in FIGS. 9A″–9C″ arepresented below.

Especially with respect to that shown in FIGS. 9A–9C and 9A″–9C″ anotherimmediately apparent distinction between the Texas Instruments deviceand those shown in the reference figures concerns what may be regardedas “dead” or “dim” space that is substantially non-reflective or poorlyreflective relative to the mirror face(s). A large central hole 118 ispresent in mirror face 80 of the former structures. As shown in FIG. 2,this actually results in a central dark or missing region in each pixelimage. By way of comparison, each mirror 126 in FIGS. 9A and 9A″ isinviolate at the center. Any dim or dead space 132 associated with theprospective mirror face only involves the space above support baseportions 148.

As alluded to above, however, depending on support configuration, thisspace may be minimized or even eliminated. Different supportconfigurations are shown in FIGS. 12A, 12B and 12C. FIG. 12A show mirrorsections 192 from above, the base 148 of each support member and wallportions 194 defining vertical sections(s) in connection with squaremirrors. FIG. 12B shows configurations advantageously employed withhexagonal mirrors as indicated by identical reference numerals. As shownin FIG. 12C, base 148 may even be altogether eliminated, especially inmirror side-mount configurations. Here, a hexagonal mirror is portrayedin which support wall(s) 134 attach directly to the underlying structurewithout the addition of an extended base portion 148. Supports 134 aredepicted in broken line because (as apparent in FIG. 9A) some thicknessof the wall resides below the surface of mirror 126 as viewed fromabove.

The manner in which producing support regions with no base is depictedin FIGS. 13A and 13B. In FIG. 13A a support precursor 196 is shown. Itis etched-out as indicated by dashed lines 198 in accordance with thediscussion above, removing region 200. The resulting, separatedstructures include support 134 and base 148 regions, with mirror regions126 above. In FIG. 13B, the support precursor region is so small thatremoval of region 200 leaves no discrete base(s) 148, but only basesurfaces 202 (attached to underlying structure).

In view of the different manner of supporting mirrors as offered byaspects of the present invention, it is possible to achieve a situationwhere between about 88% and about 100% of the prospective mirror face isutilized, and therefore comprises reflective surface. The limit for theknown devices described herein is below 88%.

Though not offering these particular advantages, the variation of theinvention shown in FIG. 9A′ offers advantages relative to the TexasInstruments approach that includes a large, central hole 118 in eachpixel. The dead or dim zones associated with mirror holes 216 asprovided in mirror faces according to the present invention are spreadapart from each other and of a combined area that is less than the TexasInstruments column support. Also, it is believed that thisdelocalization of such space will make its effects less apparent to aviewer. Decentralization of dim or dead space in the pixel may furtherdiminish the ability of a viewer to pick-out the features upon closeinspection.

However the supports are configured, as may be observed in FIGS. 11A and11B, each micromirror element is surrounded by a border 188. This gap orborder provides clearance for the mirrors as they tilt back and forth inan array. In the active regions of any micromirror array, this deadspace cannot be eliminated. It can, however, be reduced by providinglower-profile micromirror assemblies. Highly-elevated mirrors as in theTexas Instruments DMD™ that are set above a yoke 76 and greatlyseparated from the underlying hinge and/or substrate require morelateral space in which to accomplish such angular deflection as desiredthan lower profile structures as may be achieved with the presentinvention. The ability to produce low-profile micromirror devicesaccording to aspects of the present invention enables reducing overallgap or border space to less than in known micromirror devices, where gapspace is believed to represent about 11.4% of the area in the activearray region.

In certain instances reduction in gap size may be more significant thanincreasing use of prospective mirror face. For example, where shortersupports 134 are provided (or via hole 118 is more filled-in), partiallight return can be expected. In which case, the zones are more “dim”than “dead” as to reflection.

Nevertheless, the array 22 comprising Texas Instruments micromirrordevices as described is not capable of producing the resolution of array191 using micromirror devices as may be produced according to thepresent invention. In roughly the same space, array 191 packs 100 lightmodulator elements as compared to 36 in array 22. The result of thisdifference nearly triples of the number of pixels that may be projected.

The increased pixel density allows for finer detail construction of animage. Furthermore, dim or dead zones are more diffuse—and smaller (byway of smaller gaps 188 and/or spaces 132 versus holes 118). Each factorcontributes to making their effect less notable, just as they are moredifficult to discern in FIG. 11B. The fact that the overall dead spaceis less, leads to overall greater image brightness versus known devices.The distribution of the dead space over a greater number of regionsleads to greater apparent image quality. The human eye is highly attunedto pattern recognition. The dispersal of the “dead” or “dim” areas,reducing their concentration, counters this ability.

Provision of such a dramatically increased number of mirrors may,however, require certain accommodations. Considering that mirrors in aDLP™ system are controlled by loading data into the memory cell belowthe mirror, a data stream configured to actuate a lesser number ofmirrors with different addressing will typically not be suitable forrunning another array. Accommodation for such differences as presentedmay be provided by means of hardware/software. Equipment exists that cantake a given input signal at a particular resolution and either up- ordown-convert the signal to a resolution that is compatible with thedevice at hand.

In producing mirror arrays according to the present invention, asdiscussed above, mirror precursor regions are provided. These arepatterned in such a way as to provide for supports. Mirror precursorregion sections 206 are shown for three different mirror types in FIGS.14A–14C. Dashed lines are presented to indicate the location whereindividual mirror elements 126 will reside upon separation. The solidlines indicate pits or holes 132, portions of the edges will formsupport sections 134 (and possibly portions of the bottom forming bases148 as well). What may be observed is that spaces 132 reside partly inthe spaces 188 to be provided between each mirror element. Thispositioning, in effect, allows certain “theft” of space in producing thesupport structures. The reason for such a characterization stems fromprocess limitations requiring that any hole in photoresist of a givendepth must have a certain aspect ratio or size/diameter to be properlyfilled-in upon metal deposition. However, by locating open regionsduring manufacture in areas that must ultimately be left open anyway,losses of reflective space are minimized.

Regarding the various mirror configurations shown, each presents certainnoteworthy advantages that may be realized to varying degrees dependingon other material factors in array construction. These are described inturn in terms of their potential relative merits.

As to the square mirrors utilizing corner mounts, this configurationaccommodates the longest hinge length for the smallest pixel area.Especially where very small mirrors/pixels are concerned, longer hingelength can be very useful. Since for a given hinge cross-section,stiffness decreases and overall torsional displacement capabilityincreases with length, it will be possible to achieve relatively largermirror deflection using such a design. Additionally (or alternately),the additional hinge length available allows for producing the smallestpixel size possible—at least with respect to such other mirror andconnector configurations shown and discussed herein.

With the hexagonal mirrors using corner mounting points a largerrelative mirror area versus hinge length can be achieved. Such aconfiguration provides for generating greater electrostatic forces.According, reduced voltages may be applied to deflect each mirror.Reducing voltages allows a beneficial reduction in overall device powerrequirements.

Regarding the hexagonal mirrors employing side mounts, thisconfiguration accommodates a longer mirror axis perpendicular to thehinge and mirror area versus hinge length. Depending on other factors,especially hinge construction and electrode configuration, the increasedlever-arm offered by the overhanging mirror portion at the corner of themirror (as compared to the hex mirror/hinge configurations whereopposite edges are parallel to the hinge) may offer greaterelectrostatic attraction, especially toward the extremes of mirroractuation where restoring forces from the hinge are greatest. As such,this may offer relative advantages in power consumption and/or maximummirror deflection.

Further optional advantages in the invention may be realized utilizingdifferent electrode configurations. The plan or top view of electrodesmay, of course, be altered or optimized for a given situation. Moreover,FIGS. 15A–15H present side view of various potential electrodeconfigurations. Each figure shows an electrode including a plurality oflevels. In the variation in FIG. 15A two levels 152 and 154 are shown.Progressively more levels 218 are shown in FIGS. 15B–15D. In FIG. 15E, acontinuum of levels is presented in the form of a substantially uniformor angled electrode 204. Whereas the continuum of levels in FIG. 15Eprovides a simply angled surface, in FIG. 15F, an electrode with ameasure of curvature is provided. A curved section 220, may be useful intailoring electrostatic attractions between an electrode and mirror (orelectrode and any intermediate structure such as a yoke as in the TexasInstruments design) in order to match or otherwise account fornonlinearities in restoring force provided by flexure members. The curveshown is merely exemplary. However configured, curved and angledelectrode formats may be produced utilizing advanced photolithographytechniques (e.g., grayscale masking) known to those with skill in theart.

Further variation of electrode structure that is contemplated concernsproviding the various electrode levels by discrete, but electricallyconnected, members, rather than in a continuous fashion. FIGS. 15G and15H provide examples of such approaches. In FIG. 15G, level steps 222are provided, optionally supported by a column 224 with a central via228, a cantilever design 226, or any combination of electrode designsdescribed herein. In FIG. 15H, level steps 222 and angled steps 230 areprovided. Any such electrodes may be addressed individually orelectrically interconnected.

Such structures may be provided by the technique(s) described above orotherwise. For example, one method involves deposition of multiplelayers that build up the tiers. Alternatively, from a single depositionof conductive material, stepped electrodes can also be created using anindividual mask per tier. Each mask allows selective etching to definethe separate tiers of the whole electrode. Lastly, the Sandia developedSUMMiT™ technique involves a combination of these and other techniques.

Determining optimal curvature (and plan view), angle or electrodelevel(s)—relative to substrate 136—may be determined using knownempirical and/or statistical modeling or analysis techniques. The designof such aspects of the invention may account for relationship betweendesired hinge/torsion bar deflection and associated stresses, togetherwith electrostatic attractions. Certain configurations may becontemplated that have electrostatic actuation advantages for givenmirror and/or deflection characteristics. Electrode shapes, in any ofthree dimensions, may be determined via mathematical models accountingfor theoretical attractions and/or computer simulation or otherwise. Forbistable operation, the electrode shapes and nature of the models may berelatively simple. Where the intent is to provide micromirror devicessuited for control analog or beam steering techniques, more complexrelationships between mirror angular displacement, related forcing andelectrode attraction may be required.

In addition to such variation as possible in the present invention asdescribed directly and incorporated herein, other electrodeconfigurations and overall mirror and related hinge connectionconfigurations are within the scope of the present invention. In theembodiments of the invention shown and such others as may be envisioned,it can be appreciated that variation may also be presented, for example,with respect to the vertical spacing of elements.

Notably, the height or relative spacing of selected items may impact thesize and/or orientation of components such as the electrode regions.Namely, electrode shape and height may require customization to avoidinterference in meeting desired deflection ranges of the micromirror.

In any event, numerous variations and possible micromirror deviceconfigurations and related systems can be made utilizing the variousoptional features disclosed herein. These variations each presentcertain respective advantages as suitable for a given application. Someof these advantages and applications have been described merely by wayof example. Such discussion is not intended to limit the scope of thepresent invention. Indeed, certain variations of the invention coveredhereby may not even present such advantages presented above by way ofexample. Further, the invention may comprise, individually, micromirrordevices or element as described herein, just as it may encompass arraysof such structures. The applicability may depend on the intended use,many of which (but not all possible uses) have been mentioned.

In addition, it is noted that the features described herein inconnection with MEMS processing may be applied on a relatively largescale. That is to say, as used herein the term “micromirror” may beapplicable to mirror structures upwards of 1 mm indiameter/length/width. Such larger structures may find applicationsoutside the field of known projector or monitors. In all, it is to beappreciated that devices made according to the present invention may beemployed not only in the context discussed referring to displays andimage projection. Further applications may involve optical switching,adaptive optics, communications, light-shaping, photocopiers,micro-displays (such as used in mobile electronics), etc.

The breadth of the present invention is to be limited only by theliteral or equitable scope of the following claims. Efforts have beenmade to express known equivalent structures and/or features as may beapplicable. That any such item or items may not be expressed herein isnot intended to exclude coverage of the same in any way.

1. A micromirror device comprising: a substrate with electricalcomponents including address circuitry, and a micromechanical lightmodulator element comprising a mirror, wherein the mirror has a basethat is adjacent to an intermediate layer, a hinge adjacent to saidintermediate layer, and a plurality of electrodes, a first portion ofeach electrode being farther above said substrate closer to a center ofsaid mirror than a second portion of each electrode being closer to saidsubstrate further from said mirror center, thereby providing clearancefor and sequential attraction of said mirror by said electrodes, whereinsaid first portion of each electrode is in the same plane as saidintermediate layer.
 2. The device of claim 1, wherein said electricalcomponents are configured to operate each mirror in a bistable manner.3. The device of claim 1, wherein said electrodes are provided bycontinuous members.
 4. The device of claim 3, wherein at least one ofsaid continuous members is curved.
 5. The device of claim 1, whereineach of said plurality of electrodes comprises discrete members.
 6. Thedevice of claim 5, wherein said discrete members are electricallyconnected and set at different heights with respect to a substratesurface.
 7. The device of claim 1, wherein said electrodes are angledwith respect to a substrate surface.
 8. The device of claim 1, whereinsaid electrodes comprise at least two heights substantially parallel toa substrate surface.
 9. A method of making a micromirror device, saidmethod comprising: providing a substrate with electrical componentsincluding address circuitry, forming a hinge coupled to said substrate,forming a mirror having a base that is adjacent to an intermediatelayer, wherein said intermediate layer is adjacent to said hinge, andforming at least two outer electrodes on a surface of said substrate,wherein each of the outer electrodes has a first portion and a secondportion, said first portion being closer to said mirror than the secondportion and said second portion being closer to said substrate than saidfirst portion, wherein said first portion is in the same plane as saidintermediate layer, wherein said mirror is positioned for sequentialattraction by said electrodes.
 10. The method of claim 9, wherein onlyfive masks are employed in said forming acts.
 11. A micromirror devicemade according to the method of claim
 9. 12. The device of claim 11,further made according to the method of claim
 10. 13. The device ofclaim 11, wherein said electrodes are provided by continuous members.14. The device of claim 11, wherein each of said outer electrodescomprises discrete members.
 15. The device of claim 11, wherein saidelectrodes are angled with respect to a substrate surface.
 16. Thedevice of claim 11, wherein said electrodes comprise at least twoheights substantially parallel to a substrate surface.
 17. The device ofclaim 9, wherein said electrical components are configured to operateeach mirror in a bistable manner.
 18. A micromirror device comprising: asubstrate with electrical components including address circuitry, and amicromechanical light modulator element having a mirror, wherein themirror has a base that is adjacent to an intermediate layer, a hingeadjacent to said intermediate layer, and an electrode having a firstportion and a second portion, wherein said first portion is closer tosaid mirror than the second portion and said second portion is closer tosaid substrate than said first portion, wherein said first portion is inthe same plane as said intermediate layer.